Aluminum drive shaft

ABSTRACT

An aluminum drive shaft includes an aluminum alloy torque tube and aluminum alloy yokes that are pressed into each end section of the torque tube and welded to the end of the torque tube. Each end section is reduced in diameter and joined to a larger central section by a transition section. The end sections and transition sections are formed by swaging the ends of an aluminum alloy tube blank radially inwardly in two stages. The transition sections include an annular rib in the form of a concentric circular band located midway between inner and outer conical portions. The annular ribs stiffen the transition sections to reduce oil canning and noise.

[0001] This is a divisional application of U.S. patent application Ser.No. 09/027,082 filed Feb. 20, 1998 which is a continuation of U.S.patent application Ser. No. 08/743,400 filed Nov. 1, 1996, nowabandoned.

BACKGROUND OF THE INVENTION

[0002] This invention relates generally to drive shafts for automotivevehicles and more particularly to drive shafts that comprise an aluminumtorque tube and a connection member at each end of the aluminum torquetube, for connecting the drive shaft in an automotive drive line.

[0003] The use of aluminum and aluminum alloy components in place ofsteel components in automobiles is becoming increasingly popular becausea substantial weight reduction can be realized without any sacrifice instrength or durability. Moreover aluminum components are more corrosionresistant than their steel counterparts.

[0004] U.S. Pat. No. 4,527,978 granted to Barry L. Zackrisson Jul. 9,1985 discloses a drive shaft having a heat-treated aluminum alloy torquetube and a heat-treated aluminum alloy yoke or connection memberpartially telescoped within each end of the tube and joined to it bywelding. The torque tube has a constant outside diameter and a wallthickness which is constant throughout most of the length. However, thewall thickness is increased adjacent each end to compensate for reducedhardness resulting from the welding operation.

[0005] Pending U.S. patent application, Ser. No. 08/692,414 filed Aug.5, 1996 and assigned to the assignee of this invention also discloses adrive shaft having an aluminum torque tube and yokes at each end and amethod for welding the aluminum drive shaft components to each other.

[0006] The size of the aluminum torque tube used in aluminum driveshafts for automotive drive lines is determined in part by the requiredlength and torque capacity of the drive shaft. An aluminum torque tubehaving a length in the range of 5 to 6 feet, an outer diameter of 5inches, and a wall thickness of 0.083 inches is typical. The 5.0 inchouter diameter is larger than a comparable steel drive shaft. However,the end sections of the 5.0 inch outer diameter tube can be reduced indiameter and smaller yokes or other connection members can be used ateach end. This reduces space requirements at the drive shaft ends whichare usually located in crowded environments. The smaller end sectionsand yokes also reduce weight significantly particularly when the entiredrive shaft assembly is taken into account. The end sections are usuallyreduced by swaging a larger diameter tube blank.

[0007] While such aluminum drive shafts have been found to be generallysatisfactory, experience has shown that noise problems are encounteredoccasionally when thin walled tubes are used. One such noise problem isa periodic tinkling sound initiated by torque reversal when the torquetube has conical transition sections. We have determined that such asound is due to an instability phenomenon in the conical transitionsections which we characterize as oil canning and which we have found isrelated to the wall thickness of the aluminum tube.

SUMMARY OF THE INVENTION

[0008] The object of this invention is to provide an aluminum driveshaft comprising a thin walled aluminum torque tube that has reduceddiameter end sections that are connected to a larger diameter centralsection by transition sections that are stable under all normaloperating conditions.

[0009] A feature of the invention is that the aluminum drive shaftincludes a thin walled aluminum torque tube that has reduced diameterend sections that are connected to a larger diameter central section bytransition sections that have an annular rib to stiffen the transitionsections so as to reduce oil canning and noise.

[0010] Another feature of the invention is that the aluminum drive shaftincludes a thin walled aluminum torque tube that has reduced diameterend sections that are connected to a larger diameter central section bytransition sections that are formed with a concentric cylindrical bandlocated between inner and outer conical portions to stiffen thetransition sections so as to reduce oil canning and noise.

[0011] Yet another feature of the invention is that the aluminum driveshaft includes a thin walled aluminum torque tube that has reduceddiameter end sections that are of sufficient length for use in balancingthe aluminum drive shaft.

[0012] Still yet another feature of the invention is that the aluminumdrive shaft includes an aluminum torque tube that has reduced endsections and transition sections that are formed by swaging the ends ofan aluminum tube blank radially inwardly.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The above and other objects, features and advantages of theinvention will become more apparent from the following description takenin conjunction with the accompanying drawings wherein like referencesrefer to like parts and wherein:

[0014]FIG. 1 is a partially sectioned longitudinal view of a known driveshaft assembly having aluminum components including an aluminum torquetube;

[0015]FIG. 2 is an enlarged fragmentary sectional view of the driveshaft of FIG. 1 showing a reduced end portion and transition portion indetail;

[0016]FIG. 3 is a partially sectioned longitudinal view of a drive shaftassembly having aluminum components including an aluminum torque tube inaccordance with the invention; and

[0017]FIG. 4 is an enlarged fragmentary sectional view of the driveshaft assembly of FIG. 3 showing a reduced end portion and transitionportion in detail.

DESCRIPTION OF THE INVENTION

[0018] Referring now to the drawing, FIG. 1 shows a known drive shaft 10that comprises a tubular drive shaft or torque tube 12 having yokes 14at each end for installing the drive shaft 10 in a motor vehicle. Thetorque tube 12 is made from a tube of 6061 aluminum alloy thermallytreated to a T-6 condition that has a 5.0 in outer diameter and a 0.083inch wall thickness to provide the required torque capacity and otherdesired operating characteristics for a drive shaft between 5 and 6 feetin length. The torque tube 12 has a cylindrical section 16 at each endthat is reduced to a diameter of approximately 4.0 inches by a swagingprocess. This process increases the wall thickness in the end sectionsto about 0.093 inches. The yokes 14 which are also made of an aluminumalloy and preferably the same aluminum alloy are press fit in thereduced diameter end sections 16 and then welded to the end of the tubeby a circumferential weld bead 17 as shown at the right hand end inFIG. 1. Yokes 14 are used to connect drive shaft assembly 10 into anautomotive drive line by well known Cardan joints. The smaller diameterend sections 16 accommodate smaller yokes 14 and reduce spacerequirements at the drive shaft ends which are generally located in acrowded environment. Significant weight savings are also realizedparticularly when the smaller Cardan or alternative universal joints aretaken into account.

[0019] The cylindrical section 16 of reduced diameter at each end of thetorque tube 12 is joined to the larger central section 18 by transitionsections 19 that are substantially conical. These known drive shafts 10having the torque tubes 12 perform quite satisfactorily in mostinstances. However, some known drive shafts produce noise occasionally,in the nature of a periodic tinkling sound which appears to be initiatedby torque reversal. We have found that this periodic clinking sound isdue to an instability phenomenon in the conical transition sections 19which we characterize as oil canning.

[0020] In essence, the conical transition sections 19 bend back andforth between an inward concave shape and an outward convex shape asillustrated graphically by dashed line 20 and 21 in FIG. 2. This oilcanning phenomenon is related to the wall thickness and shear web of thetransition sections 19 which in the example under consideration isnominally 0.088 inches. The likelihood of the instability occurringincreases as the wall thickness of the transition section 19 decreases.We have found that the amplitude of the oil canning phenomenon thatproduces audible noise is in the range of about 0.030 to 0.045 inches oftransition deflection.

[0021] Referring now to FIG. 3 a drive shaft 110 in accordance with theinvention is disclosed. Drive shaft 110 comprises a tubular drive shaftor torque tube 112 having yokes 114 at each end for installing the driveshaft 110 in a motor vehicle. The torque tube 112 is made from a tube of6061 aluminum alloy thermally treated to a T-6 condition having an outerdiameter of approximately 5.0 inches and a wall thickness of 0.083inches in order to provide the required torque capacity and otherdesired operating characteristics. The torque tube 112 has a cylindricalsection 116 at each end that is reduced to an outer diameter ofapproximately 4.0 inches to accommodate smaller aluminum alloy yokes 114that are pressed in each end and welded.

[0022] These cylindrical end sections 116 are preferably kept at asubstantial length so that weights can be attached to the cylindricalend sections 116 to dynamically balance the drive shaft 110. Thecylindrical end section 116 would typically have a length of about 4.0inches for this purpose.

[0023] Transition sections 119 join the cylindrical sections 116 ofreduced diameter at each end to the larger central section 118. Thesetransition sections 119 are shaped to reduce oil canning significantlyif and when such an instability is encountered. More specifically, thetransition sections 119 include an annular stiffening rib that islocated between inner and outer conical portions 122 and 124 as bestshown in FIG. 4. The annular stiffening rib 120 is in the form of aconcentric circular band that has a nominal outer diameter of about 4.5inches and that is located approximately half way between the endsection 116 and the central section 118 in the radial direction and inthe longitudinal direction. The circular band which provides the annularstiffening rib 120 has a length of about 0.5 inches in the axial orlongitudinal direction.

[0024] The end sections 116 and transition sections 119 can be formed bya swaging operation in two stages. The outer conical section 124 and acylindrical section of about 4.5 inch outer diameter that extends to theend of the tube is formed in the first stage. The inner conical section122 and the fully reduced end section 116 is then formed in the secondstage leaving a concentric circular band midway between the inner andouter conical sections 122 and 124.

[0025] By shaping the transition section 119 in this manner we havereduced the amplitude of the oil canning significantly from a range ofabout 0.030-0.045 inches to a range of about 0.005-0.015 inches. Thisreduces any noise to a level that is not audible without any need forincreasing the wall thickness of the tube blank.

[0026] While this particular transition shape performs satisfactorilyfor the particular drive shaft described above, other transition shapesand/or methods of forming transitions are also possible and in someother instances may be more desirable. Also while we have illustrated atorque tube which is reduced at both ends, some drive shaft applicationsmay require a reduction at only one end section. Furthermore theinvention contemplates use of other aluminum alloys and aluminum matrixmaterials comprising an aluminum oxide and an aluminum alloy material.In other words, the invention has been described in an illustrativemanner, and it is to be understood that the terminology which has beenused is intended to be in the nature of words 20 of description ratherthan of limitation.

[0027] Obviously, many modifications and variations of the presentinvention in light of the above teachings may be made. It is, therefore,to be understood that, within the scope of the appended claims, theinvention may be practiced otherwise than as specifically described.

1. In a method of producing an automotive drive shaft in which a driveyoke is attached to the end of a hollow, elongate aluminum tube that isreduced in diameter, the improvement comprising; reducing the diameterof at least one portion of the tube to form a reduced diameter endsection and a transition section between the reduced diameter endsection and the tube, the transition section having at least threesubsections; a first conical portion attached to the reduced diameterend section; a second conical portion attached to the tube; and anannular stiffening rib between the first conical portion and the secondconical portion to stiffen the transition section; and attaching theyoke to the reduced diameter end section.
 2. In method of producing anautomotive drive shaft in which a drive yoke is attached to the end of ahollow, elongate aluminum tube that is reduced in diameter, theimprovement comprising: reducing the diameter of at least one portion ofthe tube to form a reduced diameter end section and a transition sectionbetween the reduced diameter end section and the tube, the transitionsection having an annular stiffening rib that is spaced from the tubeand the reduced diameter end section to stiffen the transition section,and attaching the yoke to the reduced diameter end section.
 3. In themethod of claim 2 wherein the annular stiffening rib is midway betweenthe cylindrical end section and the cylindrical center section in theradial direction.
 4. In the method of claim 2 wherein the annularstiffening rib is midway between the cylindrical end section and thecylindrical center section in the longitudinal direction.
 5. A method ofproducing a drive shaft for automotive vehicles having an aluminumtorque tube and a drive yoke at one end of the torque tube forconnecting the drive shaft in an automotive drive line for transmittingmechanical power, comprising: providing an aluminum torque tube having acylindrical center section of a given diameter, a cylindrical endsection of reduced diameter at one end of the torque tube for attachingthe drive yoke to the aluminum torque tube, a transition sectionconnecting the cylindrical end section to the cylindrical centersection, the transition section having inner and outer conical portionsand an annular stiffening rib in the form of a narrow concentriccylindrical band that is between the inner and outer conical portions toreduce oil canning of the transition section, the cylindrical endsection and the transition section having a length, and the cylindricalcenter section having a length that is greater than the length of thecylindrical end section and the transition section, and attaching theyoke to the reduced end section.
 6. The method of claim 5 wherein thetorque tube is made from a tube blank having an outer diametercorresponding to the given diameter of the cylindrical center sectionand the cylindrical end section and the transition section are formed byswaging an end of the tube blank, and wherein the tube blank is madefrom a material selected from the group consisting of aluminum alloy andaluminum metal matrix.
 7. The method of claim 5 wherein the cylindricalband has a length of about 0.5 inches in the longitudinal direction. 8.The method of claim 7 wherein the tube blank has an outer diameter ofabout 5.0 inches and a wall thickness of about 0.083 inches.
 9. Themethod of claim 8 wherein the drive yoke at the one end of the shaft isan aluminum drive yoke that is pressed into the cylindrical end sectionand welded to the cylindrical end section of the torque tube.
 10. Themethod of claim 9 wherein the torque tube has a second cylindrical endsection of a lesser diameter than the given diameter of the cylindricalcenter section at an opposite end of the torque tube and a secondtransition section connecting the second cylindrical end section to thecylindrical center section.